Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

need help for transistor urgently..

Status
Not open for further replies.

ankurpatel23

New Member
what is the main difference in out put of npn and pnp transistor. and other question is if we ground the emitter what will be the results for that..
 
A PNP transistor is basically the opposite of an NPN. With NPN you must bias the transistor such that there's +0.7V potential difference between base and emitter. With PNP you must bias it such that there's -0.7V potential difference between base and emitter.

If you ground the emitter, you're basically operating the transistor in "common-emitter" mode.

Brian
 
Or if you don't understand transistors at all"
The Collector on an NPN is Positive, Relative to the Emitter, with the Base Voltage Aproximately 0.6 volts above the Emitter. This is the Bias Voltage.

With a PNP, The Collector is Negative, Relative to the Emitter, with the base voltage aproximately 0.6 volts More Positive than the collector.

Hope this helps more.
 
i would say if you have a small voltage on the base of a pnp transistor the transistor will "switch on" let alot of current through the colector and emmiter. if you have a big voltage on the base it will "switch off".

a npn is the oposite
if you have a small voltage on the base it will "switch off" if there is a big voltage on the base it will "switch on".

i don't mean switch on and switch off litorally

i don't know what a bias is.

lets say im controlling a motor with a pnp transistor i ground the emmitor.
i connect the motor to 12v and to the collector then put a small current in the base the motor will turn on.

i then connect the motor to ground then the emmiter. collecter to 12v.
i put a small current in the base and the motor switches on.

i hope im right 8)
 
Bias is something that every Electronics expert knows or should know.
Bias applied to a transistor is the difference in voltage between the base and the collector. The correct voltage will make the transistor conduct or shut off. Depending on the application needed.



see this link for a better idea:
**broken link removed**

added: In a common emitter circuit as an AC amplifier.
The DC component of the base voltage is set by the voltage divider composed of R1 and R2. This is called the base "bias" voltage. Setting the base bias voltage sets the DC component of the emitter voltage, the collector current, and the collector voltage. The best bias setting is to make the DC component of the collector voltage about one-half of Vcc, which allows the largest output AC voltage swing. The maximum possible output AC voltage will then be about Vcc volts peak-to-peak. The amplifier only works well if the output peak-to-peak AC voltage is smaller than Vcc volts peak-to-peak. The output waveform will be "clipped" if you attempt to obtain a higher output voltage.

You can change the bias resistors R1 and R2, the collector resistor, Rc, the emitter resistor, Re, and the power supply voltage, Vcc.
 
Is this the blind leading the blind? ThermalRunaway is the only one who got it right (and his answer was a little ambiguous). Here's a question for the rest of you guys: Why respond to a question when you don't really know the answer?
To turn an NPN on, current needs to flow into the base. If this is the case, the base will typically be 0.6 to 0.7 volts more positive than the emitter. To turn a PNP on, current needs to flow out of the base. If this is the case, the base will typically be 0.6 to 0.7 volts more negative than the emitter.

Gary, I was baffled by your PNP answer. I think you know better.
 
danielsmusic said:
i would say if you have a small voltage on the base of a pnp transistor the transistor will "switch on" let alot of current through the colector and emmiter. if you have a big voltage on the base it will "switch off".

a npn is the oposite
if you have a small voltage on the base it will "switch off" if there is a big voltage on the base it will "switch on".

lets say im controlling a motor with a pnp transistor i ground the emmitor.
i connect the motor to 12v and to the collector then put a small current in the base the motor will turn on.

i then connect the motor to ground then the emmiter. collecter to 12v.
i put a small current in the base and the motor switches on.

Daniel - how many transistors have you blown up so far??? :shock:

Firstly, transistor are CURRENT operated, not voltage operated. Secondly, you appear to have your ideas of PNP and NPN all back-to-front!
 
Ron H said:
Here's a question for the rest of you guys: Why respond to a question when you don't really know the answer?

Ron, I really don't know the answer to your question, but I response anyway.

This is exactly the behaviour one would expect in a public forum(I've just demonstrated it :oops: ). Apparently it is also one of the few ways where one can speak out on subject one don't really know or know very little about. Another one is putting the information on a webpage. Perhaps there are more ways.

Trouble is, when people knows about 10% of something, they never realise that there are still 90% out there they have missed, or else they would have know it all, wouldn't they?
 
You shouldn't talk about voltages when describing how transistors work and are biased, except the polarity of the supply.
You should talk about currents:
An NPN transistor has a positive supply voltage for its collector current. Its base bias current is also positive.
A PNP transistor has a negative supply voltage for its collector current. Its base bias current is also negative.
So There! :lol:
 
eblc1388 said:
Ron H said:
Here's a question for the rest of you guys: Why respond to a question when you don't really know the answer?

Ron, I really don't know the answer to your question, but I response anyway.

This is exactly the behaviour one would expect in a public forum(I've just demonstrated it :oops: ). Apparently it is also one of the few ways where one can speak out on subject one don't really know or know very little about. Another one is putting the information on a webpage. Perhaps there are more ways.

Trouble is, when people knows about 10% of something, they never realise that there are still 90% out there they have missed, or else they would have know it all, wouldn't they?
My concern is that hobbyists, students, etc. post questions here, hoping to get informative answers. An incorrect answer is worse than none at all, because it can cause more confusion than being left totally in the dark.
I've said before that one needs to be aware of the limits of his knowledge, and to remain silent if he can't contribute real information. Of course, that's just my opinion. I'm probably just a cranky old fart.
 
all my transistors are fine and thats the difference i have noticed in npn and pnp. :roll:
 
Ron H said:
My concern is that hobbyists, students, etc. post questions here, hoping to get informative answers. An incorrect answer is worse than none at all, because it can cause more confusion than being left totally in the dark.

How true. The advice here is to wait for a bit before acting according to the postings and hopefully someone in the know can offer different views. Even so, the OP may still not know what the true answer is or whom to believe.

Ron said:
I've said before that one needs to be aware of the limits of his knowledge, and to remain silent if he can't contribute real information.

Only wise person observes that rule. What rule? "Knowing what's one don't know." But there is a Chinese saying, "Any three people travelling, at least one of them could be my teacher." We can learn a lot from others, even from their mistakes.
 
This is an interesting post, because I have seen so many explanations for transistors. Certainly some are innacurate or overly simplified, and others are right on. I guess I can take a shot at it from a different angle, if it helps, and get back to the point of the original post.

First of all, there are more than one kind of transistor(ie FET), but the poster seems to be referencing bipolar transistors, which are IN FACT current controlled. You need to understand how bipolar transistors are physically built, and that will lead you to understand their function. A transistor is BASICALLY two oppositely biased diodes fused together. The point at which they are connected is the base. You should know that a diode consists of two regions, one P-type material and one N-type material, and the point at which they connect is the P-N junction. You really need to study atomic chemistry with respect to silicon and germanium to understand all of this, but the structure of the N region is such that there is an excess of negative ions, and the P region is in excess of "holes". When a diode is forward biased, Being a positive voltage applied to the Anode (P region) and a lower voltage (not necessarily negative) with respect to the anode is applied to the cathode, forward conductance occurs. Reversing the diode polarity will cause only an unmentionable current, which can be considered zero, unless the avalanche voltage is exceeded. The key here is to understand that the voltage value is irrelevant, what is important is the differential between the anode and cathode. You could apply 5000 volts to the anode of a diode, and 4,995 volts to the cathode, and the same amount of current will flow as if you applied 5 and 0. This is why current is more relevant than voltage.

OK, back to the transistor, when two diodes are fused together in oppositely biased directions, you get a P-NN-P junction or a N-PP-N junction. Being the middle or base is fused, we consider it one region, so we call it PNP or NPN. Much like the diode, if a potential is applied to the base(P) of an NPN, and a lesser potential is applied to the emitter (the last N) a current will flow between these regions. Now, I can't properly explain why, but if a supply voltage is applied to the collector that is also more positive than the emitter, and the already mentioned base-emitter current is there, a proportional current will flow from the collector to the emitter. If the base-emitter current is increased, so will the collector-emitter current. THIS IS WHAT IS IMPORTANT TO UNDERSTAND. This is not at all done with voltage in the case of bipolars, it is done by changing current levels, perhaps through a resistance device that is variable..... For instance, a potentiometer can control base current which will proportionally effect collector-emitter current. If the signal applied to the base is of low amplitude, and the supply voltage at the collector is high enough in amplitude, there will be GAIN in current flow, and the tansistor becomes an AMPLIFIER. a small current controls a larger current.

Now, this is an explanation of NPN, in PNP, the opposite rules generally apply. For the base-emitter to conduct, the base has to be smaller in amplitude than the emitter, not necessarily positive or negative, just smaller in potential, and it will conduct, likewise the collector should be at a lesser potential with respect to the emitter, and all the same rules of base current controlling collector-emitter current and gain hold true.

OK, I'm exausted with typing and I think I generally described basic solid state electronics OK. PLEASE, if anyone needs to edit or expand on my comments or correct anything, please do, because I don't mean to mislead. This is just my understanding and I only hope to help someone else to understand. I didn't even go into the difference between common emitter, common base, and common collector, maybe an expert wants to add this. OK, I'm done, fire away!! LOL
 
sorry, doubleposted,

Since I doubleposted anyway, and had to delete the doublepost, I'll take this opportunity to add that an adequate explanation can't be made in just a few sentences. Like the other guys pointed out, you could write a thesis on this subject, and only describe 10% of what you need to know, and could later think of a hundred more things to add. I am absolutely not the best at explaining and putting into words what I know or understand, so I'm not sure my little paragraph is sufficient, but I certainly think it is shortcutting it to attempt an explanation in as few words as one might use to describe a rock. Heck, I think I could write a lot about rocks if I were a geologist!...LOL
 
heathtech said:
This is an interesting post, because I have seen so many explanations for transistors. Certainly some are innacurate or overly simplified, and others are right on. I guess I can take a shot at it from a different angle, if it helps, and get back to the point of the original post. First of all, there are more than one kind of transistor(ie FET), but the poster seems to be referencing bipolar transistors, which are IN FACT current controlled. You need to understand how bipolar transistors are physically built, and that will lead you to understand their function. [...rest of big block of text...more unformatted text]

Great, great info. :) Thanks!

Horrible, unreadable formatting though :( After reading such a huge paragraph, I feel like lying down and read Archie comics :p:lol:

Seriously, split that text in small paragraphs and you're my hero :cool:
 
:lol: :lol: :oops: :oops:

Sorry, I'm a tech geek, not an english major..lol'
I went back and added indentions. :wink:
 
More grist for the mill. See my previous post, as modified.
Yep Voltage is a design criteria for bias. YEP YEP YEP LOL :wink:


Current is a factor :oops: but is controlled by the collector resistors. Because you can only turn on a transistor so hard and no more current can flow than allowed by its parameters. The words voltage in respect to is a key that is stated by others in this discussion and is of paramount importance. But Hey I was trying to give a simple example without all the Technical exhaustive details. :roll:
 
1st Mil-tech said:
More grist for the mill. See my previous post, as modified.
Yep Voltage is a design criteria for bias. YEP YEP YEP LOL :wink:


Current is a factor :oops: but is controlled by the collector resistors. Because you can only turn on a transistor so hard and no more current can flow than allowed by its parameters. The words voltage in respect to is a key that is stated by others in this discussion and is of paramount importance. But Hey I was trying to give a simple example without all the Technical exhaustive details. :roll:

You are absolutely right about biasing, and get no arguement from me. But my one concern when a novice is asking a question is to clearly define the difference between voltage controlled transistors(FET) and current controlled(bipolar). To back up, though, for anyone, I mean anyone, to even grasp this concept, they truly need a good understanding of ohms law and voltage/current/resistance relationships. If you can't explain that, you have no business going any further in studying electronics. I think we can all agree on that.
We should all insist that anyone needing a tutorial needs to drill that law into their head before proceeding. After all, if you understand ohms law, you know that current doesn't exist without a voltage supply, and voltage doesn't exist without resistance.
 
danielsmusic said:
i would say if you have a small voltage on the base of a pnp transistor the transistor will "switch on" let alot of current through the colector and emmiter. if you have a big voltage on the base it will "switch off".

a npn is the oposite
if you have a small voltage on the base it will "switch off" if there is a big voltage on the base it will "switch on".

i don't mean switch on and switch off litorally

i don't know what a bias is.

lets say im controlling a motor with a pnp transistor i ground the emmitor.
i connect the motor to 12v and to the collector then put a small current in the base the motor will turn on.

i then connect the motor to ground then the emmiter. collecter to 12v.
i put a small current in the base and the motor switches on.

i hope im right 8)

I think this is the response that is so confusing, because it really doesn't explain anything or the relationship between all of the transistor terminals.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top